Packaging machines receive bag material in tubular form. Product to be packaged is delivered to the interior of the tubular bag material, with the packaging machine then transversely sealing and cutting the tubular bag material to form bags of product. The tubular bag material is formed by a former shoulder, to which packaging film is delivered in strip form. Formers and packaging machines are described in U.S. Pat. Nos. 4,910,943, 5,622,032, 4,663,917, 6,655,110, 7,159,376, 7,600,630, 7,383,672, 4,753,336, 7,124,559, 7,415,809, 7,152,387 and 7,472,528.
The tubular material provided by the former shoulder is longitudinally sealed. This function is performed by heating the tubular bag material along its longitudinally overlapping edges and by applying pressure to the overlapping longitudinal edges.
In order to successfully form the longitudinal seal, the tubular bag material must be heated to a required temperature so that upon pressure being applied the plastic material fuses to form the seal. The temperature of the tubular bag material is raised to the required temperature by the bag material passing a heated backing bar or heating bar.
The bag material is pulled past the former shoulder and delivered to the packaging machine by a film drive assembly. These assemblies have included rollers and belts with drive surfaces from which there extend passages. The passages are subjected to a reduced air pressure so that the bag material is drawn into engagement with the drive surfaces to provide for group frictional engagement between the drive surface and the bag material.
Where drive belts have been employed, the drive belts pass between an upper pulley and a lower pulley, of which one is driven. Manifolds engage the inner surface of the belt, with reduced air pressure being delivered to the manifolds which in turn communicate with the passages through the belt. The manifolds are located adjacent the length of the belt that engages tubular bag material. This length of the belt passes along a generally linear path and is generally upright.
Also located between the pulleys and located adjacent the manifolds is a heating bar that is urged against the longitudinally overlapping portions of the tubular bag material to sealingly secure the longitudinal edge portions together.
A disadvantage of the above discussed drive assemblies is that they occupy considerable longitudinal distance in the direction of travel of the tubular bag material. In particular the disadvantage is the height of the machinery, and the length of tubular bag material above the sealing jaws of the packaging machine.